1. Field of the Invention
This invention relates to biomedical systems for communicating with implanted devices such as cardiac pacemakers, muscle stimulators, drug dispensers and the like and, in particular, systems which have the capacity for providing a display of event and timing data transmitted from the implanted device.
2. Background of the Prior Art
With the increased use of programmable biomedical systems, and in particular cardiac pacing systems having an implantable pacemaker device and external programmer apparatus, there has developed an awareness of the importance of providing useful information concerning the operation of the implanted device. For example, in cardiac pacing systems, an ECG alone does not provide the doctor with the desired information, whether the ECG is obtained internally by the pacemaker or externally. There is a lot of information which can be obtained by the implanted pacemaker and transmitted for external output, which supplements the ECG information and enables the doctor to determine whether the pacemaker is operating properly, whether the selected mode is optimum, etc. Prior art biomedical systems utilizing implantable devices are known, wherein sensed diagnostic data or patient data that has been generated by the implantable device is transmitted out to external apparatus for display or other indication. For example, in the pacemaker area, it is known to have a separate analog channel for transmission of real time QRS data, the analog transmission channel being separate from and additional to the communications channel for operator programming and interrogation. While, of course, plural or even multiple channels can be used if there is no limit on expense or power requirements, there is a great need for efficient use of a single communications channel, which is capable of handling both the normal programming and interrogation requirements, as well as outputting patient and other diagnostic data.
State of the art pacemaker systems have provided for what is referred to as marker channel information which is printed in relation to an ECG so as to provide supplemental information. For example, events such as pacing or sensing of a natural heartbeat are recorded with a mark indicating the time of the event relative to the ECG. This is helpful to the physician in interpreting the ECG. Existing sytems which provide a marker channel output operate basically by outputting the pacemaker event, e.g. a delivered stimulus or sensed natural heartbeat, at about the time of the event, thereby inherently providing the timing of the event in relation to the recorded ECG. However, this arrangement places limitations upon the system capacity to output and record information concerning the wide range of events that can occur each pacing cycle, as well as desired timing information relating to the pacer operation. The requirement of continuously transmitting to the external apparatus at the time of each event or timed out interval requires a substantial amount of extra control capacity within a pacemaker, in order not to interfere with the ongoing pacemaker functioning. Thus prior art pacing systems have generally been limited to communicating simple event data, for the practical reasons of limiting the amount of circuitry which is dedicated for handling the data transmissions. This limitation is undesirable, particularly for dual chamber pacing systems, where it is desirable to provide marker channel displays for events and pacemaker timing corresponding to both the atrial and ventricular chambers. There thus exists a substantial need in the art to overcome the practical difficulties associated with real time communication, and to provide more informative and readable marker channel displays.
Applicant refers to U.S. application Ser. No. 465,891, titled "Biomedical System With Improved Means And Method For Communicating With Implanted Device", assigned to the same assignee, which is incorporated by reference. This application contains a disclosure of techniques of communication between the external programming device and the pacemaker as used in the system of the assignee of this invention, which communications arrangement forms a part of the environment of this invention. Reference is made to this application as well as to other published patent literature, for teachings as to specifics of communications methods and means employed in pacing systems, whereby data is collected by a pacemaker and transmitted from the implanted pacemaker to an external programmer device, where the data can be presented in different visual forms. The well known techniques utilized in the pacemaker industry for transmitting data from an implanted pacemaker to an external control apparatus, and vice versa, are understood to be part of the background of this invention, but as such do not form any portion of the novel features thereof.